November 9, 2020 DIRC

Meeting Information

GlueX DIRC Meeting
Monday November 9, 2020
1:00 pm, EDT
Remote only

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Agenda

1. Announcements:
2. DIRC survey results (Bill, All)
3. Optical Box inspection (Bill, All)
   • North OB slides
   • South OB slides
   • Photon yield studies (Justin)
   • Discussion of possible strategies for mirror replacement and timeline
4. South box module diagnostic and replacement plan (Bill)
5. Hall D Engineering Page: current detailed schedule
6. DIRC commissioning analyses and 2020 studies (All)
   • Spring 2020 data production status (Justin)
   • Geometric reconstruction update (Ahmed/Roman)
     • Update on shift of the time difference
   • FastDIRC update (Yunjie)
7. Follow-up on additional action items from workfest (All)
   • 100M event MC samples required for ρ and φ data/MC comparisons:
     • /volatile/halld/home/gxproj7/RunPeriod-2019-11/dircsim-2019_11-ver02/analysis/hd_root_gen_2pi_pass00.root
     • /volatile/halld/home/gxproj7/RunPeriod-2019-11/dircsim-2019_11-ver02/analysis/hd_root_gen_2k_pass00.root
8. AOB

Minutes

• Bill and Justin reported on the inspection and degraded photon yield over the Spring/Summer runs
• Discussion of mirror solutions below
• Tim suggested and we agreed to move ahead with removing the South OB mirrors some time this week for further inspection
• We agreed to remove the cookie from South OB column 18, row 2 when the FPGA board is replaced
• Roman investigated the reconstructed and true track position from the MC. As a next step, he will look at the reconstructed and true arrival time of the track.

Discussion of possible mirror solutions

• Matt suggested investigating a gasket/clamp solution to seal the surface between
  • Need to be careful with adding metal for clamps (plastic possibility), long term stability would need further investigation
  • Clamps would cover some active area and would need to have space to wrap around the back of the strong back
• Joe suggested epoxy coupling throughout may be a clean approach
  • Radiation hardness (light exposure) over time would need investigation for DP270, but Epotek 301-2 is another option
  • Need to thoroughly clean surfaces to allow capillary flow: aluminum powder to clear surfaces
  • Eugene suggested a 1-2 cm thick border of epoxy may be sufficient and maintain a some of the reflection by the air gap
• Andrew suggested a pourable epoxy over the surface of the mirror, rather than using the glass protective surface
  • Joe suggested Epotek, which is much less viscous than DP270. After the meeting I found Epotek 301-2 and 301-2FL which is apparently even less viscous.
• For evaluating further options, Matt suggested weighting the reflectivity by the incident angles of the photons to determine an average reflectivity. (Matt's note: in principle, total internal reflection makes for a perfect reflector and such reflection can be achieved over broader range of angles with an air gap.)
• Some concern about temperature variation if gluing over the full surface, possible deflection of front glass with air gap?

Proposed prototypes

Small samples (10x10cm) should be made with the following:

• Borosilicate + UVE mirror with DP270 entirely between surfaces (pump to remove bubbles?)
• Borosilicate + UVE mirror with Epotek entirely between surfaces (pump to remove bubbles?)
• Borosilicate + UVE mirror with DP270 2 cm wide strip around edge
• UVE mirror with Epotek poured on and cured over ~days under HEPA filter to investigate procedure and flatness
• UVE mirror with wipe-on screen protector

After several prototypes are made we should subject them to both water bath and UV lamp. We'll need to check with Carl Zorn if we can utilize the Big Blue Box again for reflectivity measurements.